Injection molding apparatus often include a hot runner system with a heated melt manifold. A typical method for producing a hot runner manifold is to gun drill the manifold melt channels through a solid piece of steel, machine cylindrical bores to intersect the channels, and install inserts or plugs into bores to split or redirect the manifold melt channels within the manifold or redirect the channels towards nozzle melt channels. Normally, the insert is press-fitted into the bore; however, the insert can also be brazed to the bore, or the bore and insert can be machined with mating threads so that they can be attached. The insert has a melt duct with an inlet in fluid communication with an upstream manifold melt channel and an outlet in fluid communication with a downstream manifold melt channel or nozzle melt channel. The melt duct in the insert has a generally 90° bend to redirect the melt stream.
A potential problem with the use of an insert is the risk of leakage of melt into the manifold at a junction between the duct of the insert and manifold melt channel during operation of the injection molding apparatus. This may be due to damage to the insert or corresponding bore during assembly or an imperfect fit between the insert and bore due to manufacturing errors attributable to normal machining tolerances. To minimize the risk of leakage, the insert and manifold bore in which it is seated must be machined to very strict tolerances to achieve a fluid-tight fit at operating pressures and temperatures. This precise grinding of the outer surface of the insert and the inner surface of the bore adds to manufacturing costs, and frequently results in an insert that cannot be later removed from the manifold once it is mounted.
While prior structures have proven to be satisfactory in many respects, there is still a need for more commercially advantageous structures for preventing leaks in the manifold. The present invention is intended to meet this need.